Ealing was once famous for its film comedies - but Thursday's by-election could easily rival anything committed to celluloid when it comes to bizarre plot twists and unexpected developments.

The Tories have high hopes for their candidate Tony Lit

It would be a brave pundit who predicted the outcome in this normally rock-solid Labour area following a string of defections and allegations of dirty tricks.

More than half the population in Ealing Southall comes from an ethnic minority and all of the parties, with the exception of the Greens and the Monster Raving Loony Party, are fielding candidates with an Asian background.

The area has significant Muslim and Hindu populations but Sikhs form the largest ethnic group - and the campaign has been dominated by shifting allegiances within that community.

The by-election, caused by the death of Britain's oldest MP, Piara Khabra, is certain to be seen as a test of Lib Dem leader Sir Menzies Campbell's authority, with anything less than victory or a repeat of the second place the party achieved at the 2005 general election likely to be seen as a disappointment.

EALING SOUTHALL: ETHNIC MIX

White: 37.6%

Black: 8.9%

Asian: 47%

Mixed: 2.8%

Other: 2.9%

Source: 2001 census

But it has also turned into a test of Tory leader David Cameron's efforts to modernise his party.

Conservative expectations were sky high when they unveiled their candidate, 34-year-old businessman Tony Lit.

He may have joined the Conservative Party only a few days before the start of the campaign but his high profile background - as the boss of Asian radio station Sunrise - and his smooth, media friendly style, makes him the perfect poster boy for Mr Cameron's new model Tory party.

Labour defectors

Some Tory strategists were even daring to whisper about snatching a famous victory - particularly when five Sikh Labour councillors defected to join the party.

Just over a week ago, Mr Cameron stood in triumph on Ealing Town Hall steps to unveil his latest recruits - four of whom were wearing blue turbans to mark the occasion.

Labour says the Sikh community is behind its candidate

"This is the clearest possible indication yet that the Conservative Party having been changed and modernised is now a voice for everybody," said the Tory leader.

He claimed the Conservative Party - with its belief in family, enterprise and work - was now the "natural home" for British Asians.

Labour's vice-chairman Joan Ryan, watching gloomily from across the road, declared it a "really sad day" for Labour.

She said the defectors were angry that one of their number, Gurcharan Singh, had failed to be selected as Labour candidate but had "let down" the people who had voted for them.

Blair handshake

But she said the Sikh community, which makes up about 23% of the constituency, was swinging behind Labour's candidate, Virendra Sharma, who has been a councillor in the area for more than 25 years.

Half an hour before Mr Cameron unveiled his defectors, Justice Secretary Jack Straw stood on the town hall steps to unveil Mr Sharma's latest supporter - independent candidate Kuldeep Singh Grewal who said he was throwing his weight behind the Labour man.

All of my customers vote Labour, without exception. People are used to Labour round here

But Labour did not have to wait long to be handed more substantial ammunition, when it emerged over the weekend that Mr Lit's company had last month given £4,800 to the Labour Party.

And that Mr Lit had been pictured shaking hands with former Prime Minister Tony Blair.

Mr Lit, who insists he is a lifelong Conservative sympathiser whose job as a radio station chief had prevented him from expressing his political views, was unrepentant.

The 34-year-old, who resigned from Sunrise to stand in Southall, said he attended the Labour event in his capacity "as a businessman" - and had also attended a similar Tory event.

Iraq factor

The revelation was an embarrassment for the Tory campaign in Ealing Southall but Mr Lit can still count on strong local support.

His father, Avtar, came third at the 2001 general election when he stood as an independent. He has been spotted supporting his son on the campaign trail in his dark blue Rolls Royce, with its L1 TTT number plate.

Tony Lit's election posters are everywhere - and you are never far from the sound of his campaign team's loud hailer, with its "now is the perfect time to change Ealing forever" message blaring out alternately in English and Punjabi.

Sir Menzies has been a regular on the campaign trail

But he is up against a solid Labour support base.

"Just because his father is a millionaire doesn't mean I will vote for him," said Mohammed Naseem, who runs a local barber's shop in Southall.

"We don't know anything about him. I have voted for different parties but all of my customers vote Labour, without exception. People are used to Labour round here."

But, he added, the war in Iraq was still a factor for many voters and could hurt Labour.

"Tony Blair is not a very popular man around this area. No-one likes him."

'Dirty tricks'

Liberal Democrat candidate Nigel Bakhai, who finished second here in 2005, is hoping to capitalise on the lingering anger over the Iraq war among the Asian community.

EALING SOUTHALL: RELIGION

Christian: 35%

Hindu: 12.4%

Muslim: 13.3%

Sikh: 23.3%

Source: 2001 census

His election literature features prominent pictures of Mr Blair and US president George Bush - but he is also focusing relentlessly on local issues such as crime and refuse collection and stressing that he will represent everyone in the constituency.

Lib Dem elections supremo Chris Rennard, who is overseeing the campaign from a cavernous industrial unit a stone's throw from Sunrise radio's HQ, is confident of victory.

But, he argues, the party could be hampered by a shorter campaign than normal, leaving them relying on a "late swing".

There have also been accusations of Tory dirty tricks after a message appeared on a Lib Dem YouTube page, saying: "Realistically we're not going to win . . . the Tories have stolen a march on us."

UKIP 'realist'

The Lib Dems say it was posted from the account of Tory MP Grant Shapps, who is running the campaign in Ealing Southall.

The Conservatives insist someone hacked into Mr Shapps' e-mail account in an effort to discredit him.

The Lib Dems kicked off their campaign by unveiling their own Tory defector, Brij Mohan Gupta, former deputy chair of Ealing Southall Conservatives, who accused the Tories under David Cameron of being "a party of style over substance".

Even UKIP have got in on the act by unveiling a Tory defector - William MacDougall, who contested Tottenham for the party in the last general election.

"I have been a loyal supporter of the Conservative Party for over 30 years but how can I stay when spin has replaced policy," said Mr MacDougall, explaining his decision.

The UKIP candidate, Dr KT Rajan, an NHS consultant who was born in India, is campaigning for curbs on immigration from Eastern Europe.

Climate change

"I am not being a hypocrite, I am being a realist. I am not opposed to immigration. All I am saying is it should be strictly controlled."

Mr Rajan, who arrived in the UK in 1960, is warning of the spread of disease from Eastern Europe and is calling for compulsory tuberculosis and Aids tests for new arrivals.

The anti-war Respect candidate, Salvinder Dhillon, is of Punjabi Sikh origin with much made of him coming from the constituency in his campaign literature.

Respect MP George Galloway said: "Salvinder belongs to this community. He will be Southall's man in Westminster, not Westminster's man in Southall."

The Green Party candidate Sarah Edwards - one of only two white candidates - is focusing on her opposition to the war in Iraq and climate change.

"Other parties say they are concerned about global warming, but are actively seeking to build more roads and airport runways. We will end these damaging programmes and invest in positive solutions," she said at her campaign launch.